This invention relates to lithium complex greases for rolling bearings which have high dropping points and are capable of maintaining for a long time an excellent stability of a thickener micelle under a high temperature, high adhesion, heat resistance, water resistance, rust resistance, load resistance, low noises and other high-level properties. This invention also provides a method of producing such lithium complex greases.
Because conventional greases for rolling bearings are of a relatively good heat resistance, a relatively good water resistance, less intermixing of foreign substances and a reasonable price, lithium soap greases have mainly been used in practice. However, the disadvantage of the lithium soap greases is that as its use circumstances are over 130.degree. C. (266.degree. F.) at temperature, the greases are leaked from a rolling bearing due to micelle destruction caused by oxidation, a decline of adhesive force, a grease softening, an increase of oil separation, or the like.
In order to overcome the disadvantages of the foregoing lithium soap greases, various kinds of non-soap base greases and complex greases having a very high dropping point and a heat resistance have been developed.
However, when they are used for a long time, the non-soap base greases are liable to be hardened, while the complex greases are liable to be softened extremely. Further, when a fluorine oil as a base oil is used, its price is too expensive. Accordingly, its utilization is limited.
On the other hand, the circumstances of use of the greases are becoming severer and severer in connection with miniaturization of mechanical devices and high speed of operating devices. For example, like bearings which are employed in operating equipment in an automobile, when the grease is used in the proximity of such a power source as engine, the lubricating greases for the bearings are subject to particularly high temperature conditions for a long time. In the above circumstances, the grease must have a high temperature resistance, a sufficient life durability and a water resistance. Namely, in view of various properties, it must be much more superior to the lithium soap greases as mentioned above. Today, it is demanded to develop a novelty heat-resisting grease which can assure a long life of lubrication and has removed the defects of the conventional non-soap greases and various complex greases.
Conventionally, there are known various kinds of complex greases employing various lithium soaps. Some of them are disclosed in U.S. Pat. No. 2,872,417, 2,898,296 and so on. According to U.S. Pat. No. 2,872,417, the lithium grease is produced by a base oil, a fatty acid and more excessive lithium hydroxide than an equivalent weight necessary for saponification.
After dehydration, the lithium grease is added by a phosphite ester or a phosphate ester, and a high dropping point lithium base grease is obtained.
According to various information which the inventors of this Application have so far collected, the lithium greases according to the above U.S. Pat. No. 2,872,417 have not appeared yet on the market. Further, the inventors have tested a grease sample which was produced by the compositions as described within the scope of the claims of the above U.S. Patent, and found that the grease obtained thus had no high dropping point as a heat-resisting grease.
A lithium complex grease according to U.S. Pat. No. 2,898,296 is produced by saponifying a fatty acid and a dicarboxylic acid ester with a lithium hydroxide. In this lithium complex grease, when a dicarboxylic acid is employed in lieu of the dicarboxylic acid ester, it has been confirmed that a dropping point of the grease is no more than 182.2.degree. C. (360.degree. F.) and its required purpose cannot be attained. A lithium complex grease similar to U.S. Pat. No. 2,898,296 has already been put on the market. The inventors of this Application have examined the effect of the above lithium complex grease by carrying out a heat resistance rotation test of the bearings. The result was that its lubrication life was much worse than that of a product intended by the inventors.